1. Field of the invention:
The present invention generally relates to a semiconductor memory device having a constant voltage circuit, and more particularly, the present invention relates to an erasable-programmable read-only memory (EPROM) and to a one-time programmable read-only memory (OTPROM).
This application is a counterpart of Japanese application Ser. No. 210720/1997, filed Aug. 5, 1997, the subject matter of which is incorporated herein by reference.
2. Description of the Related Art:
FIG. 2 is a circuit diagram for describing a data reading operation according to a conventional semiconductor memory device.
As shown in FIG. 2, the conventional semiconductor memory device, for example an EPROM or an OTPROM, is made up of a memory array 100 having a plurality of memory cells arranged in a matrix of rows the row select signals WL.sub.0.about.WL.sub.n applied thereto and columns having column select signals Y.sub.0.about.Y.sub.n applied thereto. The device also includes a current detecting amplifier 110 electrically connected with the memory array 100, a constant voltage circuit 120 applying a predetermined potential voltage to drains of the respective memory cells 100, and a differential amplifier 130 for amplifying outputs from the current detecting amplifier 110. The conventional semiconductor memory device uses the current detecting amplifier 110 to determine whether or not a storage charge on each of memory cells 100 is present. The conventional semiconductor memory device employs method in which a difference between currents flowing from the selected memory cells 100 to the current detecting amplifier 110 is used to determined whether or not storage charge in present in the memory cells selected by the row select signals WL.sub.0.about.WL.sub.n and column select signals Y.sub.0.about.Y.sub.n.